1. Field of the Invention
The present invention relates to a semiconductor light emitting device used for an optical recording apparatus, an optical transmission apparatus or the like, and a method for producing the same.
2. Description of the Related Art
Recently, optical recording apparatuses and optical transmission apparatuses have been used in various apparatuses in information related fields. Semiconductor laser devices used as semiconductor light emitting devices in these optical recording apparatuses and optical transmission apparatuses have been required to have high performances in terms of speed, output and the like.
As devices in information related fields are used more and more in households, the semiconductor laser devices used in these optical recording apparatuses and optical transmission apparatuses are required to be inexpensive. For example, semiconductor laser devices used in optical recording apparatuses, for example, DVD apparatuses are especially required to have high performance at low prices.
FIGS. 5A through 5D are cross-sectional views illustrating steps of a method for producing a semiconductor laser device 200 used in a DVD apparatus.
As shown in FIG. 5A, an n-type GaInP buffer layer 102, an n-type first AlGaInP clad layer 103, an undoped GaInP/AlGaInP strained multiple quantum well active layer 104, a p-type second AlGaInP clad layer 105, a p-type GaInP etching stop layer 106, a p-type third AlGaInP clad layer 107′, a p-type GaInP intermediate layer 108′, and a p-type GaAs cap layer 109′ are formed in a stacking manner in this order on an n-type GaAs substrate 101 by molecular beam epitaxy (MBE). Then, an Al2O3 layer 110′ is formed on the p-type GaAs cap layer 109′ by electron beam (EB) deposition.
Next, as shown in FIG. 5B, the p-type third AlGaInP clad layer 107′, the p-type GaInP intermediate layer 108′, the p-type GaAs cap layer 109′, and the Al2O3 layer 110′ are processed with photolithography and etching, thereby forming a striped ridge structure including a p-type third AlGaInP clad layer 107, a p-type GaInP intermediate layer 108, a p-type GaAs cap layer 109, and an Al2O3 layer 110. The striped ridge structure is formed in a central area of a top surface of the p-type GaInP etching stop layer 106.
As shown in FIG. 5C, the structure on the n-type GaAs substrate 101 is entirely rinsed with a sulfuric acid-based rinsing solution, and then washed with pure water. An n-type AlInP current confinement layer 111 is formed on the p-type GaInP etching stop layer 106 so as to cover the striped ridge structure by MBE. This step forms an unnecessary layer 112 of n-type AlInP on the Al2O3 layer 110.
As shown in FIG. 5D, the Al2O3 layer 110 and the unnecessary layer 112 are removed. A p-type GaAs contact layer 113 is formed on the p-type GaAs cap layer 109 and the n-type AlInP current confinement layer 111. Then, a p-type electrode 114 is formed on the p-type GaAs contact layer 113, and an n-type electrode 115 is formed on a bottom surface of the n-type GaAs substrate 101.
In this manner, the semiconductor laser device 200 having a waveguide with a buried ridge structure is produced.
The above-described method for producing the semiconductor laser device 200 has the following problems. Depending on the process conditions, the oscillation threshold current Ith, which is a starting point of laser oscillation, may be increased, which causes variability in the production yield of the semiconductor laser devices. This is a cause of the increased cost of semiconductor laser devices. In addition, as the oscillation threshold current Ith is increased, the malfunction rate of the semiconductor laser device is increased when continuously used for a long period of time and thus the reliability is lowered.